In early 2025, a significant vulnerability—CVE-2025-3066—was found in Google Chrome’s Site Isolation component. This bug, classified as a high severity use-after-free (UAF) issue, allowed attackers to corrupt Chrome’s memory heap by luring users to specially crafted webpages. The problem affects Chrome before version 135..7049.84. Understanding this vulnerability is crucial because of its potential to let attackers run arbitrary code on users’ computers.

In this post, we'll unpack how CVE-2025-3066 works, explore how an exploit might look, reference original advisories, and discuss mitigation.

What is a Use-After-Free Vulnerability?

A use-after-free bug happens when a piece of software keeps using memory after it has been freed. This can corrupt memory and give attackers a powerful tool to crash the program or run malicious code.

What is Site Isolation in Chrome?

Site Isolation is a Chrome security feature that separates different websites into different processes. This design helps defend against attacks like Spectre and cross-site scripting. However, if there’s a bug in how processes interact—like a use-after-free—bad things can happen.

Details of CVE-2025-3066

CVE-2025-3066 was introduced in a code refactor that affected how Site Isolation handles certain cross-origin requests and page navigations. If a remote attacker could trick a user into visiting a specially-crafted HTML page, they could trigger memory operations on already-freed objects—corrupting the process’s memory and potentially executing code.

Patched Version: 135..7049.84 and later

Reference:
- Chrome Release Notes for Stable Channel Update
- Chromium Security Advisories

Exploiting the Vulnerability

Let’s simplify how an exploit can be constructed for this kind of bug.

Suppose there’s an object in Chrome’s memory responsible for managing a cross-origin navigation. If an attacker times page operations—like opening, closing, or reloading frames—they can trigger Chrome to free this object, then operate on the dangling pointer.

Here’s a simplified pseudo-code snippet inspired by actual browsers’ code and exploitation patterns:

// Malicious HTML snippet: attacker.html
<iframe id="victimFrame" src="target_site.com/page"></iframe>
<script>
  let frame = document.getElementById('victimFrame');
  frame.onload = function () {
    // Start navigation
    frame.contentWindow.location = "about:blank";
    // While the frame is navigating, remove it from DOM (potential UAF trigger)
    document.body.removeChild(frame);
    // Allocate JavaScript objects to fill freed memory (heap spray)
    let spray = [];
    for (let i = ; i < 10000; i++) {
      spray.push(new ArrayBuffer(x10000));
    }
    // Attempt to access the freed frame reference
    try {
      let result = frame.contentWindow.someProperty;
    } catch(e) {
      // Exploit typically tries to take over this code path
    }
  }
</script>

In real exploits, the JavaScript (or WebAssembly) would be much more sophisticated, and attackers would need to bypass modern mitigations. However, this basic pattern shows the heart of a use-after-free: trigger a precise sequence of object deletions and heap sprays to fill freed memory with data under the attacker’s control.

User visits malicious website (delivered via email, ad, or compromised hosting).

2. The attacker’s page rapidly creates and destroys frames, manipulating Chrome’s Site Isolation logic.

If you manage many Chrome installs (e.g., in an enterprise), force-update via Group Policy.

- Watch for security bulletins from Google’s Chrome Releases.

References and Further Reading

- CVE-2025-3066 in MITRE
- Chrome Release Notes
- Chromium Security: Use-After-Free
- What is Site Isolation? (Google Blog)

Final Thoughts

Use-after-free bugs like CVE-2025-3066 are among the most dangerous security issues for browsers. They are hard to find, tricky to exploit, but devastating when successful. Chrome’s rapid response in fixing this bug kept users safe—as long as they updated their browser. If you haven’t already, check your Chrome version and update right now.

Timeline

Published on: 04/02/2025 01:15:37 UTC
Last modified on: 04/08/2025 20:15:28 UTC